This invention concerns stabilised aqueous peracid solutions, and processes for the preparation of such solutions. The invention particularly concerns stabilised solutions of aliphatic peracids, especially peracetic acid solutions.
Aqueous solutions of peracids have numerous applications in industry, including particularly use as bleaching agents, reagents in chemical synthesis, and especially as disinfectants for domestic, industrial and environmental applications. Many of these applications are carried out at locations removed from the location at which the peracid is produced, and thus the peracids are advantageously stable at the very least during transport to the application site. In a very large number of cases, the peracid can also be stored, for example in warehouses, for a significant period, often in the region of months or even years, prior to use.
The stability of peracid solutions can be improved by the avoidance of the introduction into the solution during its manufacture of impurities which can destabilise the peracid, notably transition metal ions. However, as a practical matter it is virtually impossible to ensure that no such impurities are present. Furthermore, even if impurities are avoided during manufacture, there remains the possibility that impurities may be introduced during any subsequent packaging or transportation of the solution. It is therefore desirable that the peracid solutions are stabilised against decomposition by such impurities. In addition to stabilising the peracid solution during storage, the presence of stabilisers in the peracid solution may also have the additional benefit of enhancing the stability of the peracid solution in use, and consequently increasing the efficacy of the solution. The presence of stabilisers can also reduce the hazardous properties of the solution.
Many systems have been proposed for use as stabilisers for peracid solutions. Amongst those which have found wide application include dipicolinic acid, for example as disclosed in U.S. Pat. No. 2,609,391. Other compounds include phosphonates, notably those disclosed in British Patent No. 925,373 Henkel. In some instances, combinations of stabilisers are employed, for example the combinations of dipicolinic acid and phosphonates disclosed in International application publication numbers. WO91/07375 and WO91/13058. Phosphates have been proposed for use as stabilicers for peracid solutions in U.S. Pat. Nos. 2,347,434 and 2,590,856. European Patent No. 0 563 584 teaches that stannates can be employed to stabilise peracid solutions provided the stannate is added to the peracid solution during or after manufacture, or is added to the reaction mixture immediately before the reaction commences. The stannate can be employed in the peracid solution in conjunction with a separately added co-stabiliser, and although a large number of potential co-stabilisers, including poly and pyrophosphoric acids and their salts are contemplated, only dipicolinic acid and 1-hydroxyethane-1,1-diphosphonic acid are exemplified. European Patent No. 0 563 584 therefore contains no teaching on the use of a stannate derivatives stabiliser for stabilising peracid solutions, nor any indication that the preparation of the stabiliser system is of any importance.
Although some stabiliser systems for peracid solutions are already known, it remains desirable to identify additional or further systems.
It is a first object of certain aspects of the present invention to provide an additional or further stabiliser system for aqueous peracid solutions.
It is a second object of further aspects of the present invention to provide a process for the production of stabilised aqueous peracid solutions.
It is a third object of yet further aspects of the invention to provide a stabiliser system which will increase the time period required for attainment of equilibrium of peracid solutions, where the peracid is present in excess of its equilibrium concentration.